Abstract

Recently, interest in the study of legged robots has increased, and various gait patterns of the robots have been established. However, unlike humans and animals, these robots still have difficulties in achieving adaptive locomotion, and a huge gap remains between them. This chapter deals with the gait transition of a biped robot from quadrupedal to bipedal locomotion. This gait transition requires drastic changes in the robot posture and the reduction of the number of supporting limbs, so the stability greatly changes during the transition. A locomotion control system is designed to achieve the gait transition based on the physiological concepts of central pattern generator, phase resetting, and kinematic synergy, and the usefulness of this control system is verified by the robot experiment.

2. Gait Transition Strategy

2.1. Problems in the Gait Transition

Because locomotor behavior is rhythmic motion, a steady gait of a legged robot indicates a stable limit cycle in the state space. Therefore, we need to control the robot to establish a limit cycle to produce a stable gait. Because different steady gaits have different stable limit cycles, a change of the gait pattern implies that the robot state moves from one limit cycle to another. Even if a robot obtains steady gaits, many difficulties remain for the gait transition.

For the gait transition, the following two issues are crucial: (1) because a robot has many Degrees Of Freedom (DOFs), it is difficult to determine how to produce robot movements to connect one gait pattern to another, in other words, how to construct adequate constraint conditions in motion planning; (2) even if the robot establishes stable gait patterns, it may fall over during the gait transition and it is difficult to establish stable gait transition without falling over.